1. Field of the Invention
This invention relates generally to programming of implantable devices, and more particularly to a programming system which addresses the dangers raised by the presence of multiple programming devices.
2. Description of the Related Art
Implantable devices have become a standard method of treating various medical conditions, many of which relate to the heart. Examples of implantable devices include pacemakers, defibrillators, nerve stimulators, drug delivery devices, and implanted personal identification chips. Many types of implantable devices are available with high capacity memories for storing data and various programmable configuration parameters. In the case of medical devices, the data to be stored may include physiological data such as the electrogram (electrical waveform of the heart detected at the electrodes), instantaneous heart rate, blood pressure, volume pumped, body temperature, etc. Configuration parameters that are stored may include modes of operation, amplifier sensitivity, filter bandwidth, adaptation algorithms, output voltages, currents and pulse widths, blanking periods, various pacing rates, circadian response patterns, lead characteristics, delay intervals, detection thresholds, safety margins, logging criteria, and error messages. As implantable devices increase in sophistication, the number of configuration parameters is also expected to increase.
Referring now to FIG. 1, a human torso 102 is shown having an implantable device 106 coupled to a heart 104. When a wand 108 from an external programming device 110 is placed in proximity to implantable device 106, the programming device 110 can establish two-way communication with implantable device 106 to retrieve data and to provide new configuration parameters. Often the device 106 collects data over a period of hours or days. In the case of a pacemaker, the data may represent measured physiological signals such as cardiac voltages (EKG signals), blood temperatures, oxygen levels, sugar levels, and other physical parameters.
Illustratively, the programming device 110 comprises an implantable device programmer and data analyzer that is used by a physician. The programmer/analyzer operates to download information stored in implantable device 106 by transmitting signals which place the pacer in a mode for downloading, and thereafter detecting signals sent by the device. Then, under control of the physician or other medical professional, the programmer/analyzer operates to analyze and display the information in a format which allows the physician to diagnose any problems. After performing an analysis, the physician may instruct the programmer/analyzer to adjust operating parameters for a different mode of operation, sensitivity setting, or other parameter value, to tailor the behavior of the device to the patient and thereby optimize the patient's quality of life. If this is the case, the programmer/analyzer 110 provides new operating parameters to the implantable device 106.
Implant manufacturers have long been aware of a danger known as the "multiple programmer" problem which can result in an implantable device having incorrect and perhaps even dangerous or harmful configuration parameters. The following scenario is presented to illustrate this problem.
A patient with an implantable device enters an examination room, and as part of a routine initial examination has a medical technician use a first programming device "A" to download data and configuration parameters from the implantable device. Depending on the amount of data and the baud rate of the device, the download time may range from 20 seconds to 20 minutes. In the absence of any gross abnormalities in the downloaded data, the patient is sent to another room for an exercise session to determine "rate modulated" settings, i.e. configuration parameters for adjusting the pacemaker pace rate in response to detecting patient exertion. In this room, a physician uses a second programming device "B" to download and adjust the configuration parameters in response to the results of the exercise session. Programming device "B" is used to reprogram the implantable device with the adjusted parameters. The patient then returns to the examination room, where a physician uses programming device "A" to adjust some of the configuration parameters in response to analysis of the downloaded data. Programming device "A" is then used to reprogram the implantable device with the adjusted parameters. It is important to note that programming device "A" is, at this point, operating with an obsolete version of the implant's configuration settings. This situation occurs whenever changes are made to the implantable device's configuration parameters by a second programming device "B" between the download and reprogramming operations of the first programming device "A".
The configuration parameters of an implantable device such as a pacemaker can individually be set to typical values within a normal operating range, but the programming device must still check for incompatible parameter settings to avoid dangerous combinations of parameter values. For example, programming an inappropriately long refractory period in conjunction with a short pacing cycle may lead to unpredictable pacing behavior. If a programming device with an obsolete version of the implant device's configuration settings reprograms only a few parameters, any safeguards that the programming device implements to avoid incompatible parameter settings could be unintentionally circumvented.
One programmer safeguard that has been employed is to have programming device "A" reprogram the implantable device with a complete set of configuration parameters rather than just the parameters which have been adjusted. Although this successfully prevents incompatible configuration settings, the previous adjustments are completely undone without any indication to the physician. Further, the reprogramming time is unnecessarily increased beyond what may be strictly necessary.
The solution commonly employed by implant manufacturers has been simply to issue warnings regarding the danger of using multiple programming devices. A more effective and inexpensive solution to the multiple programming device problem is desirable.